[SLAMGRASS] When you fuse bluegrass, there are two paths: You can do the same thing over and over again and become Mumford & Sons—sitting comfortably on a throne among the soccer moms—or you can go for broke and become Leftover Salmon, where your followers drive VW vans instead of minivans and your fame is limited, but your soul remains intact. The Boulder-born quartet has actually been doing this since 1989, when it burst onto the festival circuit as a total oddity: a bluegrass band with drums that added rock, zydeco and rootin’ tootin’ country to the mix for a sound that has since been imitated, but never at Salmon’s level, the band still going strong on last year’s Aquatic Hitchhiker.